Power supply systems are pervasive in many electronic applications from computers to automobiles. Generally, voltages within a power supply system are generated by performing a DC-DC, DC-AC, and/or AC-DC conversion by operating a switch loaded with an inductor or transformer. One class of such systems includes switched mode power supplies (SMPS). An SMPS is usually more efficient than other types of power conversion systems because power conversion is performed by controlled charging and discharging of the inductor or transformer and reduces energy lost due to power dissipation across resistive voltage drops.
An SMPS usually includes at least one switch and an inductor or transformer. Some specific topologies include buck converters, boost converters, and flyback converters, among others. A control circuit is commonly used to open and close the switch to charge and discharge the inductor or transformer. In some applications, the current supplied to the load and/or the voltage supplied to the load is controlled via a feedback loop.
For some power supply systems, a transformer is used between a primary side circuit and a secondary side circuit. In one example of an AC-DC converter for large voltages, the transformer provides isolation between the large voltage AC signal and the converted DC signal. The primary side circuit may include a rectifier and a switched converter coupled to the transformer while the secondary side may include a filter or further rectification circuit. For an SMPS, it is known that an in-rush current may be received at the input during start-up. Such an in-rush current may damage the SMPS if not properly handled during start-up.